U.S. patent number 6,988,143 [Application Number 10/220,499] was granted by the patent office on 2006-01-17 for processing network address identifiers.
This patent grant is currently assigned to British Telecommunications. Invention is credited to Shaun S Baker, Caroline M Beauchamps, Philip M Clarke, Paul J Felton, Alan W O'Neill.
United States Patent |
6,988,143 |
O'Neill , et al. |
January 17, 2006 |
Processing network address identifiers
Abstract
The invention provides a method, data processing system and
software for generating address identifiers for use in a
communications network. The method comprises the step of processing
a first address identifier constructed in accordance with a first
communications protocol; and the step of constructing a second
address identifier, from said first identifier, in accordance with
a second communications protocol. The first communications protocol
may be protocol Simple Mail Transfer Protocol (SMTP) and the second
communications Session Initiation Protocol (SIP). The invention
enables messages to be sent to a SIP URL derived from an SMTP email
URL. In the event that the SIP URL is invalid, or unregistered the
SIP message is diverted from a SIP defined destination URL address
identifier to a corresponding SMTP defined destination URL address
identifier for the same user or end system. In this way users may
send SIP messages to SMTP address identifiers using the SMTP
network protocol and infrastructure (416) and SMTP messages to SIP
address identifiers using the SIP network protocol and
infrastructure (408, 410, 412).
Inventors: |
O'Neill; Alan W (Ipswich,
GB), Clarke; Philip M (Ipswich, GB), Baker;
Shaun S (Zurich, CH), Beauchamps; Caroline M
(Hertfordshire, GB), Felton; Paul J (Suffolk,
GB) |
Assignee: |
British Telecommunications
(London, GB)
|
Family
ID: |
8172822 |
Appl.
No.: |
10/220,499 |
Filed: |
March 26, 2001 |
PCT
Filed: |
March 26, 2001 |
PCT No.: |
PCT/GB01/01331 |
371(c)(1),(2),(4) Date: |
August 30, 2002 |
PCT
Pub. No.: |
WO01/74029 |
PCT
Pub. Date: |
October 04, 2001 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20030046405 A1 |
Mar 6, 2003 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 24, 2000 [EP] |
|
|
00302425 |
|
Current U.S.
Class: |
709/230;
709/221 |
Current CPC
Class: |
H04L
29/06 (20130101); H04L 29/12009 (20130101); H04L
61/00 (20130101); H04L 69/16 (20130101); H04L
69/169 (20130101); H04L 69/08 (20130101); H04L
69/327 (20130101) |
Current International
Class: |
G06F
13/00 (20060101) |
Field of
Search: |
;709/200-203,217-224,230-231 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Meky; Moustafa M.
Attorney, Agent or Firm: Nixon & Vanderhye P.C.
Claims
What is claimed is:
1. A method of operating a network to provide communications in
accordance with a first communications protocol, said method
comprising: receiving a base address identifier convertible by a
first directory server associated with said network to an address
for use in communications made in accordance with a second
communications protocol; derive, from said base address identifier,
an amended address identifier convertible by a second directory
server to an address for use in communications made in accordance
with said first communications protocol; wherein at least part of
said address identifiers is formed in accordance with a
hierarchical addressing scheme, said part comprising a sequence of
address identifier components, the position of a component in said
sequence indicating the level of said component in said
hierarchical addressing scheme; said method being characterised in
that said derivation involves providing amended address components
so that a plurality of base address identifiers convertible by said
first directory server are converted to one or more amended address
identifiers convertible by said second directory server.
2. A method according to claim 1 wherein at least one of said one
or more address components is positioned in said sequence such that
in said amended address identifier, said one or more added address
components are associated with higher positions in said hierarchy
than the address components derived from said base address
identifier.
3. A method according to claim 1 in which one or more of said base
address identifier components are maintained in said amended
address identifier.
4. A method according to claim 3 in which all of said base address
identifier components are maintained in said amended address
identifier.
Description
This application is the US national phase of international
application PCT/GB01/01331 filed Mar. 26, 2001 which designated the
U.S.
This invention relates to a method of operating a communications
network.
The Session Initiation Protocol (SIP) is an application-layer
control protocol for creating, modifying and terminating sessions
having one or more participants. These sessions include Internet
multimedia conferences, Internet telephone calls and multimedia
distribution. Members in a session can communicate via multicast or
via a mesh of unicast relations, or a combination of these. SIP
supports session descriptions that allow participants to agree on a
set of compatible media types. It also supports user mobility by
proxying and redirecting requests to the user's current location.
SIP is not tied to any particular conference control protocol.
There is widespread interest in the protocol, especially for
telephony-related applications. SIP was proposed by the Internet
Engineering Task Force (IETF) group and is now a proposed standard
published as RFC 2543.
The entities used in SIP are user agents, proxy servers, redirect
servers and location servers. A SIP user agent is an end-system
that allows a user to participate in a session. A SIP user agent
contains both a user agent client and a user agent server. A user
agent client is used to initiate a session and a user agent server
is used to respond to request from a user agent client. A user is
addressed using an email-like address identifier "user@host", where
"user" is a user name or phone number and "host" is a domain name
or numerical Internet Protocol (IP) address. SIP defines a number
of request types, in particular INVITE, ACK, BYE, OPTIONS, CANCEL,
and REGISTER. Responses to SIP messages indicate success or
failure, distinguished by status codes, 1xx (100 to 199) for
progress updates, 2xx for success, 3xx for redirection, and higher
numbers for failure. Each new SIP transaction has a unique call
identifier (call ID), which identifies the session. If the session
needs to be modified, e.g. for adding another media, the same call
identifier is used as in the initial request, in order to indicate
that this is a modification of an existing session.
The SIP user agent has two basic functions: listening for incoming
SIP messages, and sending SIP messages upon user actions or
incoming messages. The SIP user agent typically also starts
appropriate applications according to the session that has been
established. A SIP proxy server can relay SIP messages--it is
possible to use a domain name to find a SIP proxy server, for
example using the Domain Name System (DNS), rather than knowing the
IP address or name of the host. A SIP proxy can thereby also be
used to hide the location of the user. A redirect server returns
the location of the host rather than relaying the SIP message. Both
redirect and proxy servers accept registrations from users, in
which the current location of the user is given. The user's
location can be stored at a dedicated location server.
SIP is typically implemented by transmitting Internet Protocol (IP)
packets. SIP is independent of the packet layer and only requires
an unreliable datagram service, as it provides its own reliability
mechanism. While SIP typically is used over UDP or TCP, it could be
used over frame relay, ATM AAL5 or X.25.
SIP is a text based protocol and is based to a certain extent (in
terms of syntax) on the HTTP protocol. A typical message consists
of a single request line, a number of header lines and a message
body.
The request line indicates the type of the messages, the message
destination and the SIP version it complies with. The following is
a typical example:
INVITE sip:Richard@bt.com SIP/2.0
A header line contains the name of the header type, followed by a
semicolon and the contents as these are defined for the specific
header. Consequently, each header type is used for a specific
purpose (either to indicate some parameters or to issue a request).
The following are typical examples:
From: sip:Richard@bt.com
To: sip:Steve@bt.com
Subject: Official meeting
The message body may be of any content, although it usually has
contents formatted in accordance with the Session Description
Protocol (SDP).
SIP URL address identifiers such as sip:Richard@bt.com are required
for the exchange of SIP messages in a similar way that e-mail URL
address identifiers are required for the exchange of electronic
mail.
By using an e-mail type address it is possible to deliver a SIP
message to a SIP server that knows the location of the user or user
agent server the message is intended for. The IP address of the SIP
server having authority for the callee's address can be readily
determined by DNS. The above referenced proposed standard, RFC
2543, encourages implementers of SIP services to name SIP servers
by appending the string `sip.` to their domain name. It is further
suggested that an implementation might derive an address for use in
SIP communications from the intended recipient's e-mail address.
The proposed method of derivation is to add the prefix `sip.` to
the host part of the intended recipient's e-mail address (e-mail
addresses normally being of the form `user@host`).
According to an aspect of the present invention there is provided a
method of operating a network to provide communications in
accordance with a first communications protocol, said method
comprising:
receiving a base address identifier convertible by a first
directory server associated with said network to an address for use
in communications made in accordance with a second communications
protocol;
derive, from said base address identifier, an amended address
identifier convertible by a second directory server to an address
for use in communications made in accordance with said first
communications protocol;
wherein at least part of said address identifiers is formed in
accordance with a hierarchical addressing scheme, said part
comprising a sequence of address identifier components, the
position of a component in said sequence indicating the level of
said component in said hierarchical addressing scheme;
said method being characterised in that said derivation involves
introducing amended address components so that a plurality of base
address identifiers convertible by said first directory server are
converted to one or more amended address identifiers convertible by
said second directory server.
In this way, it is possible to derive unique address identifiers
for new communications services to be provided over a newly
implemented communications protocol from respective address
identifiers provided for services associated with a fully
implemented communications protocol. The above method provides for
a new address space to be created for use with DNS or other address
resolution systems for the provision of communication services
associated with a newly available communications protocol. The
invention also provides for translation between address spaces. For
instance, if a message is sent but not delivered to a user or
location identified by an address identifier generated in
accordance with the above method, the address identifier can be
resolved back to its respective original address identifier and the
message sent to the location associated with that original address
by means of a service available over the first communications
protocol. In this respect, address resolution is readily achievable
since the respective first and second address identifiers are
directly derivable from one another. This avoids the usual
requirement of providing and maintaining of a costly address
database for mapping respective first and second address
identifiers. Another advantage of the above method is that the
address space is readily scalable. For instance, by using the
domain name hierarchy associated with the first communications
protocol a new domain name hierarchy can be created and integrated,
if appropriate, with DNS. A further advantage of the above method
is that users can readily address messages etc, for transmission
over one communications protocol using an address identifier
associated with another communication protocol. The ability to make
use of the address space associated with a widely implemented
communications protocol is very important when, say, new services
are to be introduced using a new protocol. For example, a user may
address a message to another user using a new address identifier
derived from a known identifier regardless of whether the user is
aware of the recipient's address identifier for the newly
introduced protocol or whether the recipient has indeed been
allocated a new address identifier or is capable of receiving the
message over the new protocol. The user sending the message only
requires knowledge of the recipient's address identifier associated
with the widely implemented protocol.
In contrast to the RFC 2543 proposal of adding an address component
at the lowest level of the domain name hierarchy, the present
invention provides address components at a higher level than the
lowest level component in the known e-mail address. The entries in
the directory can be concentrated in the directory server
associated with the level of the hierarchy that corresponds to the
added address component. Where, as is normally the case, there are
a plurality of instances of address components below the added
address component, this enables the directory service for the first
communications service to be provided by a single directory server
rather than a plurality of directory servers.
Preferably, at least one of said one or more address components is
positioned in said sequence such that in said amended address
identifier, said one or more added address components are
associated with higher positions in said hierarchy than the address
components derived from said base address identifier.
This has the advantage that all directory enquiries can be handled
by a directory server under the control of a party introducing said
first communications service.
In some embodiments, the base address identifier components are
removed and replaced by amended address identifier components.
However, in preferred embodiments, one or more base address
components are maintained in said amended address identifier. This
allows address hierarchies which have evolved in relation to the
base address identifier to be re-used in the provision of the
second communications protocol.
If all the components of the base address identifier are maintained
in the amended address identifier, then this gives the advantage
that an address (e.g. an e-mail address) which is known to be
unique in relation to the second communications protocol is also
known to be unique in relation to the first communications
protocol. In addition, the base address identifier can be
re-created from the amended address identifier, thus allowing the
second directory server to revert to the second communications
protocol if desired and forward a message intended to be sent in
accordance with the first communications protocol in accordance
with the second communications protocol instead. This allows, for
example, the second directory server, on receiving a SIP message
for which it is unable to provide an address, to instead send an
e-mail to the intended recipient indicated that it has been unable
to provide a SIP connection through to the recipient.
According to another aspect of the present invention, there is
provided a method of generating address identifiers for use in a
communications network; said method comprising the steps of:
processing a first address identifier constructed in accordance
with a first communications protocol; and,
constructing a second address identifier, from said first
identifier, in accordance with a second communications
protocol.
Preferably, said first identifier is processed in accordance with a
pre-determined set of rules to provide said second identifier.
Conveniently, said first identifier comprises at least one address
component and said second identifier comprises at least one address
component of said first identifier. In this way address components
can be common to both first and second address identifiers.
In preferred embodiments, said second identifier includes each
address component of said first identifier. This simplifies address
translation and allows users to intuitively derive one address
identifier from the other identifier. This enhances the integration
of services provided over a newly introduced communications
protocol with services provided over an existing communications
protocol.
Preferably, said step of constructing said second identifier
comprises the step of adding one or more address components to said
first identifier. This enhances the above mentioned advantages.
Conveniently, said method comprises the steps of adding at least
one prefix address component and at least one suffix address
component to said first identifier. This provides for the addition
of at least two further distinguishing address components.
In preferred embodiments, said prefix address component is
representative of the second communications protocol and said
suffix component is representative of a network domain associated
with said second network communications protocol. This allows users
to identify the communications protocol that is associated with the
newly generated address identifier and the network domain authority
for that address identifier.
Preferably, said second communications protocol is an application
layer control protocol. This provides for the implementation of
user applications and new communications services over said
communications protocol.
Conveniently, the control protocol conforms to Session Initiation
Protocol. Thus SIP messages can be addressed to an existing address
identifier, for example and e-mail address identifier constructed
in accordance with Simple Mail Transfer Protocol (SMTP), and
translated to a corresponding SIP address identifier for
transmission to a SIP user agent server regardless of whether the
SIP address identifier is known to the user. Thus, the present
invention enables messages to be readily diverted from a SIP
defined destination URL address identifier to a corresponding SMTP
defined destination URL address identifier for the same user or end
system. In this way users may send SIP messages to SMTP address
identifiers using the SMTP network protocol and infrastructure and
SMTP messages to SIP address identifiers using the SIP network
protocol and infrastructure.
In preferred embodiments, a software program is arranged to
implement the method according to the above-described aspect of the
invention.
According to another aspect of the invention there is provided a
system for generating address identifiers for use in a
communications network; said system comprising:
a processor for processing a first address identifier constructed
in accordance with a first communications protocol; and,
an address identifier constructor for constructing a second address
identifier, from said first identifier, in accordance with a second
communications protocol.
The invention will now be described with reference to the
accompanying drawings in which:
FIG. 1a is a schematic representation of a typical SIP message
signalling sequence in a network comprising a SIP re-direct
server;
FIG. 1b is a schematic representation of a typical SIP message
signalling sequence in a network comprising a SIP proxy server;
FIG. 2 is a block diagram of a SIP user agent;
FIG. 3 is a block diagram of a SIP user agent graphical user
interface;
FIG. 4 is a schematic representation of a communications network
comprising a plurality of SIP enabled network domains; and,
FIG. 5 is a flow diagram of a method implemented in the
communications network of FIG. 4;
With reference to the drawings, typical signalling sequences are
shown in FIGS. 1a and 1b between two user agents 100 and 102
connected over a communications network using a SIP redirect server
106 (FIG. 1a), and a SIP proxy server 108 (FIG. 1b). In both
arrangements a SIP location server 110 is connected to the
respective SIP network server for address resolution.
In FIG. 1a, user agent 100 sends a SIP Invite message 112 to user
agent 102. The Invite message is received at and processed by the
re-direct server 106 to determine the network location of user
agent 102. The re-direct server sends a location query 114 to the
location server 110. The location server determines the current
network location of user agent 102 and sends this information to
the re-direct server in a message 116 for transmission to the user
agent 100 in a message 118. User agent 100 then sends an Invite
message 120 to user agent 102, either directly or via other SIP
re-direct or proxy servers, which then responds by sending an
acceptance message 122 to the user agent 100. User agent 100
completes the session or call set up procedure by sending an
acknowledgement 124. Once the session has been set up information
can be exchanged between the respective user agents.
In FIG. 1b, user agent 100 sends a SIP Invite message 126 to user
agent 102 as before but instead of being processed by a re-direct
server the message is processed by the network proxy server 108.
The proxy server sends a location query 128 to the location server
110. The location server determines the current network location of
the user agent 102 and sends this information back to the proxy
server in a message 130. The proxy server then relays the Invite
message to the user agent 102 by means of a message 132 which is
processed by the user agent 102. A call acceptance message 134 is
then sent back to the proxy server which relays a corresponding
message 136 to the user agent 100. The user agent 100 then sends an
acknowledgement message 138 to the proxy server which similarly
relays a corresponding message 140 to the user agent 102.
With reference now to FIG. 2, a typical SIP user agent 200
comprises a front end system in the form of a graphical user
interface (GUI) 202, a SIP client program 204, a SIP server program
206, a media module 208, a network interface 210 a SIP address
cache 212, a SIP URL address generator 214 and a SIP message
processor 216.
A typical SIP GUI is shown in FIG. 3. The GUI 202 comprises a
plurality of buttons 302 to 310 each of which represents a
different SIP request method. Button 302 represents the SIP
"INVITE" request for inviting a callee to a SIP session, button 304
represents the "OPTIONS" request for discovering the capabilities
of the receiving terminal, button 306 represents the "BYE" request
for terminating a call or a call request, button 308 represents the
"CANCEL" request for terminating incomplete call requests and
button 310 represents the "REGISTER" request method for registering
the current location of the user with a respective domain location
database 110. The respective request methods are invoked by a user
clicking the respective button, by mouse controlled cursor click or
otherwise. The GUI further comprises a text box 314 labelled "To:
SIP URL" for user input, by keyboard entry or address book entry
selection for example, of the SIP address identifier of an intended
callee, that is to say the SIP destination message header field
"To"; a text box 316 labelled "To: e-mail URL" for user input of
the e-mail address identifier of the intended callee; and, a text
box 318 labelled "Title" for displaying title information to
identify the session. A further text box 320 is provided for the
input of other SIP message text including for example other SIP
header types and text comprising the SIP message body. Text may be
input into any one of the text boxes 314, 316, 318, 320 using known
text processing means, for example, keyboard entry, selection from
pull down menus or cut and paste text processing applications.
The SIP message constructor is configured to process data entered
into any one of the boxes 314, 316, 320, 320 and construct a SIP
message including the relevant request type for transmission to an
appropriate SIP network server. For example, the message
constructor copies the text entered in the text box 314 to the SIP
message header type "To:" in the SIP message being constructed.
Other header types are determined by the message constructor such
as "Content-type:" and "Content length:" for example.
The user agent client program is configured to initiate a SIP
session or "call" and the user agent server program is configured
to respond to a call. In this regard the user agent client program
implements the SIP request methods Invite, Options, Bye, Cancel and
Register, and the user agent server implements the methods Invite,
Bye, Cancel and Ack methods. Messages are passed from the user
agent client to the network interface 210 for transmission to the
intended callee associated with the destination SIP URL address.
SIP messages are received at the destination end by the network
interface and are processing by the user agent server. The media
module 208 provides the necessary API's for sending system calls to
appropriate media applications for processing different media types
once a SIP session has been established.
When a user wishes to initiate a SIP session, the user interacts
with the GUI 202 to construct a SIP Invite message including a
destination SIP or e-mail address. Once all the necessary data has
been input to the GUI, including the SIP header types and message
body, the message processor constructs an appropriate SIP message
for transmission to the callee. In the event that the callee's SIP
URL address is unknown to the user, the user inputs the callee's
SMTP e-mail address in the text box 316. The e-mail address is then
sent to the SIP URL generator 214.
The SIP URL generator 214 comprises a software program for
generating a SIP URL address identifier from a respective SMTP
e-mail address identifier for a respective user.
The SIP URL generator is configured to process the e-mail address
identifier, in accordance with a set of pre-determined rules, to
generate a corresponding SIP URL address identifier for the callee.
In one arrangement, the e-mail address is processed by the SIP URL
generator which adds a prefix address component to the existing
e-mail address components "user@host" etc. The prefix address
component identifies the communications protocol that the new URL
is to be used with. In this embodiment "sip" is added as a prefix.
A suffix address component is also added to identify a SIP domain
name authority the newly generated SIP URL address identifier is to
be identified with. In one example the SIP URL generator is
configured to process the SMTP e-mail address "alan.oneill@bt.com"
to derive the SIP URL address identifier
"sip:alan.oneill@bt.com.sipit.com", that is to say, to add the
protocol prefix "sip" and the domain suffix "sipit.com" to the
existing SMTP readable e-mail address "alan.oneill@bt.com". Thus,
the SIP URL generator is configured to generate SIP URL address
identifiers by processing a respective address identifier
constructed in accordance with the Internet e-mail communications
protocol SMTP. In another example the SIP URL generator is
configured to process the same SMTP e-mail address identifier to
derive the SIP URL address identifier
"sip:alan.oneill@bt.com.uk.sipit.com", that is to say a
geographical identifier "uk" is additionally added to the SMTP
e-mail address identifier. The additional geographic identifier may
assist scalability of the name space and hence network routing
efficiency of the resulting SIP message, for example.
Referring now to FIG. 4, a plurality of network domains 400, 402
and 404 are each connected to the Internet 406 by means of a
respective SIP network server 408, 410 and 412. In the network of
FIG. 4 the SIP network servers are configured for use both as SIP
proxy and SIP re-direct servers. The SIP network servers provide
access to and from the respective domains. Each network domain
comprises a plurality of SIP user agents 200(a g). SIP user agents
200a, 200b and 200c are connected to the network server 408 in the
domain 400, SIP user agents 200d, and 200e are connected to the
network server 410 in the domain 402, and SIP user agents 200f and
200g are connected to the network server 412 in the domain 404.
Each SIP network server is connected to a respective location
server 110 for SIP address resolution and an associated SIP to SMTP
e-mail gateway 414. Each SMTP e-mail gateway is connected to a
respective SMTP Mail Transfer Agent (MTA) 416 for relaying SMTP
e-mail messages to respective destination SMTP MTA's over transport
layer TCP connections.
Each SIP to SMTP e-mail gateway 414 comprises an SMTP e-mail
address generator 418 and a message processor 420 which comprises
an SMTP user agent. The e-mail address generator comprises software
for generating an SMTP address identifier from a SIP URL address
identifier. In this regard the e-mail address generator is
configured in a similar but reverse manner to the address generator
214. The e-mail address generator is configured to process the SIP
URL destination address identifier of an out going SIP message to
derive a corresponding SMTP e-mail address identifier. The e-mail
address generator processes the SIP URL address in accordance with
the same pre-determined set of rules as the SIP address generator
214, but processes these rules in reverse order with respect to the
address generator 214. For instance, in one embodiment a SIP
message arriving at the SIP to SMTP e-mail gateway 414 is parsed to
determine the destination SIP URL. The SIP URL is then passed to
the SIP to e-mail address generator 418. The remaining part of the
SIP message is re-formatted by the message processor 420 into SMTP
format suitable for transmission as an SMTP e-mail message.
In one embodiment the address generator 418 is programmed in
accordance with the above set of rules, that is to say to remove
the protocol identifier prefix "sip" from the SIP URL address and
to remove the sip domain suffix component "sipit.com". The address
generator sends the re-formatted SMTP address identifier to the
message processor where the newly derived SMTP address is added to
the re-formatted message as the destination SMTP address for that
message. The message processor adds the newly generated SMTP
address to the SMTP "To:" header field of a respective SMTP
message. For example, the address generator 418 is programmed to
derive the SMTP e-mail address identifier alan.oneill@bt.com from
SIP URL "sip:alan.oneill@bt.com.sipit.com".
The message processor 420 constructs an appropriate SMTP message
for transmission to the newly generated SMTP address according to
the content of the respective SIP control message. For example, the
SIP message payload, for example the SDP message component of the
SIP message , is added as text to the respective SMTP message body
for transmission to the respective destination SMTP address. In the
example described with reference to FIG. 3, the SDP text shown in
box 320 is processed and added as text to the SMPT message payload
by the message processor 420.
With reference now to the flow diagram of FIG. 5, a user initiates
a SIP session in step 500 by interaction with the GUI 202 of a SIP
user agent 200. A data entry for each of the required data types is
input by the user including a destination SIP address in box 314
or, in the absence of a known SIP URL for the intended recipient,
an SMTP e-mail address that is known to be allocated to the
recipient in box 316. Data relating to the SIP message is processed
into SIP format by the SIP message processor 216 and is then
submitted to the user agent client 204 by the user selecting the
Invite button 302 by mouse click or other data input command. The
user agent client determines in step 502 whether a SIP URL address
has been provided or an SMTP e-mail address. If a SIP URL has been
provided processing proceeds to step 508. However, if an SMTP
e-mail address identifier has been provided the user agent client
sends the e-mail address to the address generator 214 for
processing to a respective SIP URL address identifier in step 504.
A respective SIP URL is generated in accordance with the above
described method. In step 506 the newly derived SIP URL address is
added to the SIP destination header type "To:" following the INVITE
request type of the SIP message.
The SIP message is transmitted to the appropriate local SIP network
server 408, 410 or 412 in step 508 to be relayed or re-directed to
a network server associated with the destination SIP URL address.
The network server that receives the SIP message queries its
associated location database 110 in step 510, using DNS or other
address resolution means, to determine the network server the SIP
message should be transmitted to. In step 512 a network server
having authority for the domain for the destination SIP URL
determines whether the destination SIP URL address is a valid
network address, that is to say, whether the SIP URL address has
been allocated by the domain authority to a SIP user. The SIP URL
destination address is a valid network address if it can be
resolved by a location database using DNS or other resolution means
to a respective numerical IP address, for example. In this respect
address resolution may involve querying other location databases
associated with other network SIP servers or SIP domains in a
similar way that DNS resolves numerical IP addresses. In step 514,
if the destination SIP URL address is valid, that is to say it has
been allocated to a respective user and can be resolved, the
location server returns the IP address of the next SIP server that
is configured to relay or re-direct the message or if appropriate
the IP address of the end system currently associated with the
destination SIP URL. The SIP message is sent to the next SIP
network server or destination end system in step 516. If the SIP
URL is invalid, that is to say it has not been allocated by the
appropriate domain authority for use in the network, an appropriate
SIP network server transmits the SIP message to an associated SIP
to SMTP e-mail gateway in step 516. The destination SIP URL may be
invalid for instance because it was automatically generated from a
known e-mail address identifier in step 504 and no corresponding
SIP address exists. Under these circumstances the message processor
420 re-formats the SIP message to an SMTP message for communication
over the Internet 406 in accordance with SMTP in step 518. In step
520 the destination SIP URL address is processed by the address
generator 418 in step 520 to derive the SMTP e-mail address
encapsulated within the SIP URL address. Additional information and
data is added to the re-formatted SMTP e-mail message in step 522
including, for example the text: "You were called by SIP user
<sender's SIP URL and associated data> at <time, date>
with message <SIP message body content (SDP)> but you were
not found in the SIP registration system. You can register at
<http hyperlink> where you can download a SIP client." or,
"You were called by SIP user <sender's SIP URL and associated
data> at <time, date> with message <SIP message body
content (SDP)> but you were not found in the SIP registration
system. You can register using the attached http form <http
registration form with mailto: URI address>. A SIP client
<SIP client executable code> is attached."
The SMTP message is sent to an associated mail transfer agent 416
in step 524 for transmission to the e-mail address derived in step
520 using the SMTP network protocol. In step 526 the sender is
informed by the SIP server that the destination SIP URL was not
valid and that the message was instead re-formatted according to
SMTP and sent to the SMTP e-mail address derived in step 520.
It will be seen that the other embodiments of the present invention
could be readily implemented by the skilled person, for instance
instead of the SIP message being diverted to a SIP to e-mail
gateway in the event that the destination SIP URL address is
invalid, a SIP message could be readily diverted to a SIP to e-mail
gateway if the user or the end system associated with the user was
unavailable or unwilling to receive SIP messages at the time of
message transmission. In one embodiment, the respective SIP server
selects an appropriate message from an associated message library
(not shown) for inclusion with the original SIP message in step
522. The message library includes a respective delivery failure
message for each SIP message delivery failure mode, including for
example, destination SIP user agent unavailable, user unavailable,
network connection failure, user unwilling to join SIP session or
user unwilling to join designated sessions, user will be available
at <time, date>, etc.
It will also be seen that in other embodiments the SIP to e-mail
gateway 414 could be readily implemented in other network devices
such as a respective network SIP server or a SIP user agent.
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